Flash Flood Warning 44, NWS Honolulu, HI

776 
WGHW70 PHFO 290648
FFSHFO

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE HONOLULU HI
848 PM HST TUE MAY 28 2013

HIC003-290800-
/O.CON.PHFO.FF.W.0044.000000T0000Z-130529T0800Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
HONOLULU HI-
848 PM HST TUE MAY 28 2013

...A FLASH FLOOD WARNING REMAINS IN EFFECT FOR THE ISLAND OF OAHU IN
HONOLULU COUNTY UNTIL 1000 PM HST...

RADAR CONTINUES TO SHOW HEAVY RAIN OVER THE KOOLAU RANGE WITH 
RAINFALL RATES IN EXCESS OF 2 INCHES PER HOUR. THE PUNALUU STREAM 
GAGE WAS AT 7 FT...THE KAHANA STREAM GAGE AT 6 FT AND THE NORTH FORK 
OF THE KAUKONAHUA STREAM WAS APPROACHING 10 FT AT 845 PM. THE AREA 
OF HEAVY RAIN REMAINS NEARLY STATIONARY.

LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO PUNALUU...
WAIKANE...LAIE...KAAAWA...KAHUKU AND HAUULA.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A FLASH FLOOD WARNING MEANS FLASH FLOODING IS IMMINENT OR OCCURRING
IN STREAMS...ROADS AND LOW LYING AREAS. MOVE TO HIGHER GROUND NOW.

DO NOT CROSS FAST FLOWING OR RISING WATER IN YOUR VEHICLE OR ON FOOT.
TURN AROUND...DON/T DROWN.

&&

THIS WARNING MAY NEED TO BE EXTENDED BEYOND 1000 PM HST IF FLASH
FLOODING PERSISTS.

LAT...LON 2161 15806 2173 15796 2133 15769 2129 15784

$$

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
344 PM HST TUE MAY 28 2013

.SYNOPSIS...
AN UPPER LOW NEAR THE ISLANDS...WHICH LED TO LOCALLY VERY HEAVY
RAINFALL OVER THE STATE TODAY...WILL BE SLOWLY MOVING AWAY TONIGHT
AND WEDNESDAY. A MORE STABLE AIRMASS WILL ALLOW FOR A GRADUAL TREND
TOWARD FEWER SHOWERS FOR WEDNESDAY AND THURSDAY. A WEAK RIDGE OF
HIGH PRESSURE TO OUR NORTH WILL KEEP WINDS ON THE LIGHTER SIDE THE
NEXT FEW DAYS. THE RIDGE IS EXPECTED TO STRENGTHEN THIS WEEKEND...
WITH AN UPTICK IN TRADES EXPECTED.

&&

.DISCUSSION...
A RATHER LARGE AND BROAD UPPER LOW JUST NE OF THE ISLANDS HAS
RESULTED IN LOCALIZED VERY IMPRESSIVE RAINFALL TOTALS SO FAR
TODAY. NEARLY 16 INCHES OF RAIN /15.73/ AT MOANALUA AND OVER 14
INCHES /14.39/ AT HARANO TUNNEL JUST IN THE LAST 12 HOURS.
MEANWHILE...RAIN GAUGES JUST A FEW MILES AWAY HAD ALMOST NOTHING.
THESE RAINS HAVE LARGELY FALLEN OVER AREAS WHICH ARE USED TO
SEEING HEAVY RAIN...ALTHOUGH NOT QUITE THIS HEAVY.

IN ADDITION TO THE OROGRAPHICALLY FORCED...ANCHORED DOWNPOURS...
SOME HEFTY AFTERNOON CONVECTION HAS BLOWN UP OVER SOME LEE AREAS.
LIGHTNING DETECTION NETWORKS HAVE EVEN INDICATED A HANDFUL OF
STRIKES OVER THE INTERIOR SECTIONS OF THE BIG ISLAND. THE 00Z
SOUNDINGS CONFIRMED HOW UNSTABLE IT WAS...SHOWING SURFACE BASED
CAPE /SBCAPE/ OF ABOUT 1150 J/KG AT PHLI...AND 1750 J/KG AT PHTO.

THE MODELS ARE IN GOOD AGREEMENT THAT THE UPPER LOW WILL BEGIN TO
SHIFT AWAY FROM THE ISLANDS AS EARLY AS TONIGHT. EXPECTING A LOT
OF THE ACTIVITY TO WEAKEN WITH THE ONSET OF EVENING LAND BREEZES.
IT IS VERY DIFFICULT TO SAY WHETHER OR NOT WINDWARD AREAS WILL
COMPLETELY CLEAR OUT. IF THE GRADIENT WEAKENS FURTHER AS SUGGESTED
BY SOME MODELS...THEN WINDWARD AREAS MIGHT NOT SEE MUCH RAIN LATER
TONIGHT. ON THE OTHER HAND IF THE SYNOPTIC GRADIENT IS STRONG
ENOUGH TO KEEP THE MOIST ESE WINDS GOING...THEN SHOWERS COULD DEVELOP
OR MOVE ASHORE. GOING TO LEAN MORE TOWARDS THE LATTER SCENARIO FOR
NOW FOR THE SMALLER ISLANDS...AND MORE TOWARD THE FORMER SCENARIO
FOR THE BIG ISLAND.

THE NEXT COUPLE OF DAYS SHOULD FEATURE A GRADUAL TREND TOWARD MORE
SETTLED WEATHER AS THE UPPER LOW MOVES AWAY. AT THE SURFACE...A WEAK
SUBTROPICAL RIDGE TO THE N WILL KEEP TRADE WINDS AT BAY. SOME AFTERNOON
CONVECTION WILL BLOW UP OVER THE ISLAND INTERIORS WED AFTERNOON...
BUT SHOWERS SHOULD NOT SHOULD BE AS HEFTY OR AS NUMEROUS AS TODAY.
FEWER SHOWERS ARE EXPECTED THU AFTERNOON. THERE SHOULD BE CONSIDERABLE
CLEARING EACH NIGHT FOR THE CENTRAL AND LEEWARD SECTIONS.

BY THE WEEKEND...THE SUBTROPICAL RIDGE TO THE N SHOULD REESTABLISH
ITSELF ENOUGH TO BRING MODERATE TRADES BACK TO THE ISLANDS. MODELS
SHOW A DIGGING UPPER TROUGH TO THE W OF THE ISLANDS FRI THROUGH
SUN. THIS WILL BRING INCREASING SW FLOW AND HIGH LEVEL MOISTURE
OVER THE ISLANDS. HAVE ADJUSTED THE SKY GRIDS FOR THE WEEKEND TO
BE CLOUDIER OVER PORTIONS OF THE STATE USING A BLEND OF THE HIGH
LEVEL RH FIELDS.

&&

.AVIATION...
AIRMET SIERRA REMAINS IN EFFECT FOR MTN OBSC OVER WINDWARD AND MAUKA
AREAS OF OAHU MOLOKAI MAUI AND THE BIG ISLAND DUE TO MVFR CIGS AND
SHRA. AMPLE MOISTURE HAS COMBINED WITH WEAK FLOW AND INSTABILITY TO
CAUSE AREAS OF MTN OBSC. ELSEWHERE...VFR CONDITIONS WILL
PREVAIL...EXCEPT IN THE VICINITY OF WINDWARD SLOPES WHERE ISOL MVFR
COND AND BRIEF MTN OBSC WILL OCCUR IN SHOWERS. THE SHOWERS WILL
DECREASE OVERNIGHT ALLOWING THE AIRMET TO EXPIRE...TIMING HOWEVER
NOT CERTAIN.

ALSO...THE INSTABILITY HAS ALLOWED THUNDERSTORMS TO DEVELOP OVER THE
BIG ISLAND. THE CONVECTION SHOULD DIMINISH AFTER SUNSET.

&&

.MARINE...
WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH THE WORK WEEK. THE SURFACE RIDGE REBUILDS NORTH OF THE
STATE BY THE WEEKEND...AND WINDS ARE EXPECTED TO INCREASE AGAIN
DURING THE WEEKEND. SMALL CRAFT CONDITIONS ARE POSSIBLE ACROSS THE
TYPICALLY WINDIER AREAS NEAR MAUI AND THE BIG ISLAND IF THE MODEL
SOLUTIONS HOLD TRUE.

SMALL SWELLS ORIGINATING FROM THE SOUTHERN HEMISPHERE WILL CONTINUE
TO MAINTAIN BACKGROUND SURF ALONG SOUTH FACING SHORES THIS WEEK. A
SMALL LONG PERIOD SOUTHWEST SWELL ARRIVING LATE FRIDAY MAY PRODUCE A
SMALL BUMP IN SURF HEIGHTS ALONG SOUTH FACING SHORES THIS WEEKEND. A
LARGER SOUTH SWELL MAY ARRIVE LATE MONDAY INTO TUESDAY. ELSEWHERE...
A MODERATE EASTERLY TRADE SWELL WILL SLOWLY SUBSIDE THROUGH THE
WEEK AS THE TRADE WINDS WEAKEN...THEN PICK UP AGAIN TO MODERATE
LEVELS OVER THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION...R BALLARD
AVIATION...EVANS/WROE
MARINE...BRAVENDER